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qcow2: Batch flushes for COW 

qcow2 calls bdrv_flush() after performing COW in order to ensure that the
L2 table change is never written before the copy is safe on disk. Now that the
L2 table is cached, we can wait with flushing until we write out the next L2
table.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2011-01-14 15:55:38 +01:00
parent 29c1a7301a
commit 3de0a2944b
3 changed files with 19 additions and 4 deletions
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20
block/qcow2-cache.c
View File

@ -38,6 +38,7 @@ struct Qcow2Cache {
int size;
Qcow2CachedTable* entries;
struct Qcow2Cache* depends;
bool depends_on_flush;
bool writethrough;
};
@ -85,13 +86,15 @@ static int qcow2_cache_flush_dependency(BlockDriverState *bs, Qcow2Cache *c)
}
c->depends = NULL;
c->depends_on_flush = false;
return 0;
}
static int qcow2_cache_entry_flush(BlockDriverState *bs, Qcow2Cache *c, int i)
{
BDRVQcowState *s = bs->opaque;
int ret;
int ret = 0;
if (!c->entries[i].dirty || !c->entries[i].offset) {
return 0;
@ -99,11 +102,17 @@ static int qcow2_cache_entry_flush(BlockDriverState *bs, Qcow2Cache *c, int i)
if (c->depends) {
ret = qcow2_cache_flush_dependency(bs, c);
if (ret < 0) {
return ret;
} else if (c->depends_on_flush) {
ret = bdrv_flush(bs->file);
if (ret >= 0) {
c->depends_on_flush = false;
}
}
if (ret < 0) {
return ret;
}
if (c == s->refcount_block_cache) {
BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_UPDATE_PART);
} else if (c == s->l2_table_cache) {
@ -167,6 +176,11 @@ int qcow2_cache_set_dependency(BlockDriverState *bs, Qcow2Cache *c,
return 0;
}
void qcow2_cache_depends_on_flush(Qcow2Cache *c)
{
c->depends_on_flush = true;
}
static int qcow2_cache_find_entry_to_replace(Qcow2Cache *c)
{
int i;

2
block/qcow2-cluster.c
View File

@ -637,7 +637,7 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
* handled.
*/
if (cow) {
bdrv_flush(bs->file);
qcow2_cache_depends_on_flush(s->l2_table_cache);
}
qcow2_cache_set_dependency(bs, s->l2_table_cache, s->refcount_block_cache);

1
block/qcow2.h
View File

@ -229,6 +229,7 @@ void qcow2_cache_entry_mark_dirty(Qcow2Cache *c, void *table);
int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c);
int qcow2_cache_set_dependency(BlockDriverState *bs, Qcow2Cache *c,
Qcow2Cache *dependency);
void qcow2_cache_depends_on_flush(Qcow2Cache *c);
int qcow2_cache_get(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
void **table);